The present invention relates to color printers of the thermal transfer type for printing a gradated image in the form of collective image elements according to image bit data, and more specifically relates to a data processor thereof for processing input image bit data to output image bit data for direct use in the printer.
Normally, individual image elements printed by a thermal transfer printer cannot be gradated individually due to its specific feature. Therefore, in order to print the gradated image, the image density is made in terms of a number of printed image elements per unit section. On the other hand, an original gradated image to be reproduced by the thermal transfer printer is normally comprised of collective image elements which are individually gradated. The collective image elements which are individually gradated are represented by a train of image bit data gradated correspondingly to the individually gradated image elements.
Accordingly, the original train of image bit data cannot be used directly in the thermal transfer printer. It is necessary to convert the original train of image bit data for use in the thermal transfer printer. Conventionally, such conversion is normally carried out externally of the printer. An image data source comprised of personal computer etc. and connected to the printer conventionally carries out such conversion before feeding the train of image bit data to the printer.
However, the personal computer requires a considerably long processing time to convert the image bit data, because the personal computer has to arithmetically process the image bit data bit by bit according to a given program or software. Thus, the conventional external data processing device is not practically matched to the high speed thermal transfer color printer.